In designing an apparatus for pinpointing sparking RF interference sources on high-voltage and extra-high-voltage power lines, the following considerations were made:
Point sources of high-level corona radiation are almost always present on EHV (extra-high-voltage) lines, those operating at 345 kV and above, and are frequently present on HV (high-voltage) lines, those operating at 115 kV and above).
Such corona is not usually the cause of radio and television interference complaints. Sparking is found to be the source of 95% of such complaints originating from power-line sources. For this reason it is important to know whether the RF noise sources are caused by corona or sparking. Then, if the sparking source(s) only are located and corrected, the complaints are usually resolved. (Sparking sources radiate broadband RF energy up to at least 600 MHz and sometimes to above 1000 MHz.)
Any metallic object, such as a locating antenna, brought up close to a high voltage conductor will tend to exhibit "self-corona," that is, corona will form on, and radiate corona plumes (visible in the dark) from such objects and also radiate electromagnetic waves, resulting from this corona. This RF noise, when resulting from corona, is not detectable by the locator of this invention above 20 MHz.
Even though the antenna and receiver are intended to receive noise-signals at the UHF frequency of 400 MHz, for example, if RF corona currents get inside the metal case housing the receiver, such corona RF currents may be picked up in the IF (intermediate frequency) stages of said receiver-said stages operating at a much lower frequency, such as at 10 MHz. This 10 MHz noise-signal picked up will then be detected along with said 400 MHz noise-signal.
A short metal rod antenna of perhaps a few inches in length was determined by the inventor to be most suitable for the proximity detection (or sniffer-type locating) intended. Here there is a self-corona problem, however, as noted in the above paragraph. Such a rod may be fixed or extensible, but should be designed so as not to go into corona when brought up close to an EHV conductor.
I decided in my invention to use an extensible rod antenna, because I could then also use it as a sensitivity control. Also, my goal was to make the apparatus as simple to operate as possible-with only one control. This is accomplished.
The self-corona problem on the slidable extensible rod antenna is overcome by using a part metal, part plastic rod. Said rod is plastic in the top portion and metal in the lower (as shown in FIG. 2). A knob of tubular plastic on the top of said rod and fastened with plastic screws is used to move the metal-plastic rod in and out. Using the proper plastic (nylon in the prototype) provides a sturdy and practical assembly, with said metal portion being the active antenna and said plastic portion being the manual-operating and self-corona-limiting portion. Here the top portion also prevents accidental metal-to-metal contact with the conductor with resultant arcing.
The metal-plastic rod is also found to be of advantage in the use of the rod as a sensitivity control.
It was found in the prototype that by using the rod antenna as a sensitivity control the sensitivity could be reduced to almost zero as desired, but that (not as desired) adjustment of sensitivity as the rod was pushed in was difficult because large changes in sensitivity resulted from very small changes in rod extension, particularly as the said apparatus was brought up close to a source. When close to a noise-signal source, the search is made with low sensitivity settings.
This sensitivity control problem was corrected by constructing (after some experimentation) an attenuation collar which permits suitably small changes in sensitivity to be made with reasonable changes in rod extension. Said attenuation collar is shown in FIG. 2. Here the air space inside the attenuation-collar may be considered as having less "RF field density" than that outside, and moving the junction of the metal-to-plastic of the rod down and through this airspace and partially into the housing provides suitably small steps of attenuation. Use of this attenuation-collar also permits full attenuation down to zero sensitivity. These attenuation steps are indexed on the rod, with the cursor being considered the top surface of the attenuation collar.
Because of the intended use of the device at EHV voltages, which requires longer hot sticks than used with my prior art apparatus disclosed in U.S. Pat. No. 4,439,723, my present invention is designed for use with standard solid core hot sticks rather than hollow core hot sticks as used with my prior art apparatus. Said standard solid core hot sticks are less flexible and more manageable in long lengths than the special shorter hollow hot stick. Said hollow hot sticks with sound conducted through the hot stick tubing and being emitted at the operator end are very practical at distribution voltages, but not at EHV voltages.
The longer hot stick lengths used require more audio output from the housing speaker than required in said prior art device in order that the noise signal may be satisfactorily heard at the hot stick operator's position, at the other (lower) end of the hot stick. This requires more battery power, and this is supplied by adequate batteries which may be recharged from a vehicle charging source.
Although no method for use of my prior apparatus, U.S. Pat. No. 4,439,723, is claimed in the patent, the design concept for locating is described in paragraph 3 of its Summary of the Invention: "Another object of this invention is the provision of an electrical systems defect detector and locator of the class described which functions rapidly first to locate the general area of a defect source by VHF sniffing and then immediately thereafter to pinpoint the defect source by ultrasonic sniffing."
In my present invention no ultrasonic function is used, and both the area-locating and the pinpointing phase of the operation are done with UHF sniffing; I also refer to "sniffing" as proximity detection.
These two functions are possible because of the excellent attenuation features of said antenna rod and attenuation collar assembly and because of the characteristic radiation of noise signals at 430 MHz and other UHF frequencies. Because of the much shorter wavelength at 430 MHz rather than at the 110 MHz of my prior art device, the area of significant radiation is confined to a much smaller area on the power line or structure.
The references cited as a possible challenge to my application of May 11, 1981 for my prior patent have been reviewed and these appear to have even less merit as a challenge to my present application, with the possible exception of Beasley, U.S. Pat. No. 3,820,018. Beasley shows a locator which can operate at a frequency of 450 MHz; however, it is not suitable for hot stick use. The instruments required, described but not illustrated, would weigh at least five pounds and would also be too bulky for hot stick use.
Beasley uses various antennas for four separate frequency channels. The smallest of these in his FIG. 4 could be used if it had a detector and amplifier attached for operation at 450 MHz; this would not be practical for hot stick use.
Using a yagi antenna at UHF frequencies from a bucket truck, as suggested by Beasley, has been tried by the myself and others, but it is not a suitable method of pinpointing a source on a structure; it is awkward and unreliable for identifying a point source, and in most real situations working with line crews it would not be done.